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Date: Thu, 18 Apr 2013 09:37:12 +0200
From: Stefan Hajnoczi <stefanha@gmail.com>
Message-ID: <20130418073712.GC19195@stefanha-thinkpad.redhat.com>
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Subject: Re: [Qemu-devel] [PATCH v7] sheepdog: add discard/trim support for
 sheepdog
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To: Liu Yuan <namei.unix@gmail.com>
Cc: Kevin Wolf <kwolf@redhat.com>, sheepdog@lists.wpkg.org, qemu-devel@nongnu.org, Stefan Hajnoczi <stefanha@redhat.com>, Paolo Bonzini <pbonzini@redhat.com>, MORITA Kazutaka <morita.kazutaka@lab.ntt.co.jp>

On Thu, Apr 18, 2013 at 01:50:53PM +0800, Liu Yuan wrote:
> @@ -184,6 +186,8 @@ typedef struct SheepdogInode {
>      uint32_t data_vdi_id[MAX_DATA_OBJS];
>  } SheepdogInode;
>  
> +static bool discard_supported = true;

Normally state should be part of BDRVSheepdogState so that it does not
affect other sheepdog drives.

Please confirm that all -drive file=sheepdog:... must either support
discard or not support it.  I asked this in an older version of the
patch but wasn't sure if my question was clear.

Imagine a scenario where you run two sheepdog clusters and want to
connect one drive from each cluster to your VM.  If one cluster uses
outdated sheepdog software but the other is up-to-date, then it should
still be possible to use discard on the up-to-date cluster.

Stefan